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cylonlover writes with news of an update to the model used for calculating the habitable zone around stars shifting things out a bit. From the article: "Researchers at Penn state have developed a new method for calculating the habitable zone (original paper, PDF) around stars. The computer model based on new greenhouse gas databases provides a tool to better estimate which extrasolar planets with sufficient atmospheric pressure might be able to maintain liquid water on their surface. The new model indicates that some of the nearly 300 possible Earth-like planets previously identified might be too close to their stars to to be habitable. It also places the Solar System's habitable zone between 0.99 AU (92 million mi, 148 million km) and 1.70 AU (158 million mi, 254 million km) from the Sun. Since the Earth orbits the Sun at an average distance of one AU, this puts us at the very edge of the habitable zone."

I don't see how moving the moon into a higher orbit would change the earth-sun dynamic. If the moon's further away, it'll just have a smaller average tidal effect. It'll pull the earth less in all directions assuming the orbital eccentricity remains the same.

The earth and moon orbit around the combined center of mass (barycenter: http://en.wikipedia.org/wiki/Barycenter#Astronomy [wikipedia.org]). Moving the moon moves that center of mass. Though it's not a necessarily efficient method to move the earth; the assumption is that the earth-moon system is in a stable orbit. Move one hard enough in the wrong way, and it may destabilize to where the model doesn't work. Also, destabilizing the moon's orbit could be a potential hazard.

I once calculated this out, in fact. We need to move the Earth a bit over 2 feet per year to outdistance projected solar warming as our sun ages. This is within theoretical limits of our technology to accomplish in the next few hundred years.

The other option is to make an artificial ring to block out about 1% of The Sun's energy.

Gravity is an inverse square force - if you move the moon away from the earth it would have less effect . You could knock the moon completely out of the solar system and the earth would remain pretty much in the same orbit. (Space 1999 anyone?)

You probably mean more like our entire combined worldwide nuclear arsenal all going off at once in a single location.

Even then, I doubt it would have enough effect. The earth has been hit by countless enormous hunks of rock during its creation, each with power in the multitudes of times greater than our arsenal, and they didn't manage to move the world.

The earth has been hit by countless enormous hunks of rock during its creation, each with power in the multitudes of times greater than our arsenal, and they didn't manage to move the world.

That's patently false. If any mass hits the earth, we move. How much? Depends on how much mass hit us, but we certainly move. There isn't a threshold where we start moving over a certain amount of mass, the question is how much we move based on the force that was exerted on the planet and the mass of the planet. If anything at all hits us, that number is never exactly 0.

Not directly related, but the XKCD "What If" scenario on just changing the rotation of the earth enough to avoid having leap-seconds would require 50,000 4m diameter rocky asteroids hitting the earth every second.

Back-of-a-fag-packet calculations that every nuclear and non-nuclear explosion in the history of civilisation wouldn't give enough oomph to move us more than a few km away from the sun (although that didn't stop anyone making films about it). http://www.imdb.com/title/tt0054790/ [imdb.com]

This then suggests a simple fix for global warming - we just need to move Earth into a slightly higher orbit.

Nah, we could simply drop a giant ice-cube into the ocean every now and then. Of course since the greenhouse gasses are still building up it will take more and more ice each time, thus solving the problem once and for all!

You may think you are jesting but... my husband works in the nuclear industry and the nuclear plant down near New Orleans gets it's water intake that it uses for cooling from the Mississippi River. One summer they had record highs and the electric company was making money hand over fist running the plant because demand was at record highs. It was hot enough that the temperature of the water they were pulling out of the river was getting too high for them to keep running the plant at the current output and

If the goal is a nuclear winter, sure. If you're trying to move the planet... how can I put this as succinctly as possible: If we detonated every nuke we had on one side of the planet, we'd succeed only in leaving one side of the planet uninhabitable. It wouldn't move the planet by any appreciable amount. The subsequent earthquakes would probably do more, by affecting spin. People seem to forget in orbital mechanics, to move in one direction, you have to displace an equal amount of mass x energy in the opposite direction. All a nuke would do is move the air around and leave a hole in the ground. Nothing would be ejected into space, and therefore, no movement.

I know you're trying to be funny, but after awhile, I get tired of the "a nuke is powerful enough to do anything!" thinking. I blame Bruce Willis.

I get tired of the "a nuke is powerful enough to do anything!" thinking. I blame Bruce Willis.

My Organic instructor was a real math geek, one day she demonstrated that a quarter inch of rain falling on Manhattan resulted in the same release of energy as the atomic bomb dropped on Hiroshima, she was good at estimating cube roots of 4 digit numbers in her head too.

Changing the orbits of planets is probably not a simple as you think. There are resonances between the orbits of planets of the Solar System which would change because of the move. Who knows what that would do? The length of the year would increase and it would take biological systems time to adapt. I don't know that it would affect the length of a day but if we have the power to move the planet we certainly have the power to set the length of a day to anything we want within reason.

If we had a petawatt worth of power plants (presumably fusion)why would we need to worry about global warming - shut down all the fossil fuel burning power plants and use some of that power to pull the excess CO2 out of the atmosphere.

Not from the plants, from all the equipment using that energy. One area of energy abundance many over look is the heat generated by its consumption. While we are moving away from some obvious sources; incandescence bulbs many others still exist.

Niven's way ahead of you. It's a simple matter of knocking Uranus into a cometary orbit and using its gravity to move Earth further out.

I'm reading Larry Niven's "A World Out Of Time" now (after another slashdotter recomended it), and I'm almost where this is going to be explained. Good read so far, page 72 and it's already 3 million years into the future!

I thought the same thing, and then I thought: Not Niven, he wouldn't write something so dumb. So I googled and found this:

In Larry Niven's World Out of Time, somebody built one very big fusion ramscoop and dropped it into Uranus' atmosphere. It grabbed compressed hydrogen on the way down, then "bounced" back up to the upper atmosphere where it fired it all off in a directed fusion blast, which pushed it back down into the lower atmosphere where the whole process was repeated. Uranus was thus turned into a planetary gravity tug which was used to move Earth and Mars around (sun was heating up, I think -- it's been a few years).

(source [orbiter-forum.com]) I don't think that would pass proper physics audit, but... there have been stupider ideas in scifi books.

For Earth Day 2012 we are mobilizing the planet simply to say one thing: the Earth won't wait. It seems that environmental issues have been put on the back burner as we are in the midst of a global recession. It is time for us to Mobilize the Earth

However, I was disappointed when their implementation did not even begin to approach my own vision. [google.com]

This then suggests a simple fix for global warming - we just need to move Earth into a slightly higher orbit.

Larry Niven already proposed this four decades ago in his novel Ringworld [amazon.com] , where the alien race the Puppeteers had moved their planets away from their sun to cool them. This was long before fears of global warming, but Niven felt that technological advancement would inevitably lead to problems with waste heat.

Hmm, not in my definition of "few hundred". The calculation is actually easy to make:

The earth is about 1,5E11 m away from the Sun, let's say that 1% is the variation that we want, so we get it to 1,515E11 m. So the difference in energy that we need is GMm(1/R1-1/R2) \approx 5E31 J; quite a lot.

The best (or worst, depending on your point of view) nuke we ever exploded is the Tsar Bomba [wikipedia.org], which was 57 megatons or better 2,4E17 J.

So if we managed to use this energy with 100% efficiency (which we obviously can't) to move the Earth, we would need 10^14 nukes. Well, guess we're stuck here.

If we can get a small asteroid to gradually move a bigger asteroid around the solar system in a controlled orbit, then we could make such asteroid steal momentum from Jupiter or Saturn bit by bit to put Earth's orbit out a bit more. It would take several thousands of years, though. It's within our current technology because we just to use smaller objects to move & control progressively bigger objects by leveraging the big planets. It's somewhat similar to how we used Jupiter's gravity to speed up the Ne

Well, given a thousand years or so we could probably dump enough asteroid material on it to bring the mass up. By then, we should have enough fusion tech to scarf hydrogen from Jupiter, fuse some of it up to oxygen, fuse more up to nitrogen, and combine the rest with some of the oxygen for water. Then seed with microbes, algae, etc; that ought to take another few hundred years. But after all that, sure, Mars ought to be nice.

And by the time that's done with we could probably set up a Nivenesque drive syst

Nah, fission on Mars to split Fe to O2/N2. And we'd probably need to pull it into the asteroid belt to get all the asteroids to it, and we'd need nearly the entire belt to get it a noticeable gain in mass.

And I'd use the Niven drive to push all the gas giants together. See how star-like the result is. Then move that gas super-giant towards earth, and set Earth, Mars, Venus, and all the Jovian moons around, crashing Europa into Mars for the mass/water, and then using the Niven drive to move the small sta

The whole "Earth is fine-tuned for life" stuff has been debunked for ages (but still circulates thanks to creationists), but it's pretty amazing to consider our planet could be more than 1.5 times as far out as it is now, and still remain habitable.

Also, note that the Earth's perihelion places us at 0.983AU. If these numbers are correct, our orbit actually leaves the habitable zone for a brief period every year.

Grab those guns, stock up on the freeze dried. Hunker down, it's gonna be a wild ride!

(Remember, this is a pretty soft call, lots of things in the model that aren't accounted for: clouds for one. Don't get all worked up just yet. In the end, we're our own worst enemy, the Universe is merely indifferent.)

You do realize that the habitable zone has been moving out over the life of the solar system? The Sun converts hydrogen to helium, helium is more dense, increasing the density of the Sun causing it to burn hotter. Estimates are that some billion years ago the Sun was 25% cooler which would have shrunk the habitable zone quite a bit, perhaps to the point where Venus was habitable. Also with the Sun getting hotter, in perhaps half a billion years the oceans will boil and the Earth will be much more similar to Venus.

Of course as you moved the orbit out the Earth would be colder and the the evolved biosphere would likely be very different than it is now. The habitable zone doesn't mean it's necessarily habitable for humans, just life in general.

They were making a valid point about how this would indicate we are not right in the middle of a goldilocks zone, which one would expect if creationism were true.

Why would you expect that? There is no reason, other than an attempt at trying to prove a scientific explanation for something by trying to put artificial limits on the metaphysical one. You can't disprove creation by saying "it wasn't done the way I would have done it were I God", any more than you can prove something was done using a specific scientifically supported method by saying "that's how I would do it were I Isaac Newton."

Pointing out the wrongness and the scientific illiteracy of a viewpoint is not bigotry; it is a favor. Every bit of evidence and explanation that people give you to answer your claims represents work put in by rational and compassionate human beings, at no expectation of reward, in order to improve your knowledge and understanding of this world we live in. Because that is what science is for.You may want to cut down on the arrogance and start being grateful any time now.

Surface? No, but Europa is believed to have an icy surface hiding a massive liquid water ocean. Although it is far from the habitable zone, gravitational interactions with Jupiter generates heat which keeps the oceans liquid. Add in some organic materials (which asteroids might supply) and life could have developed deep under the surface of Europa. Perhaps right now, as I type this, some big Europan fish-like creature is swimming through the cold oceans on the moon. (Or perhaps there are just Europan bacteria... even single celled alien life would be a major find.)

Mars had liquid water at some point and is outside the habitable zone, for some definitions of habitable zone. So it is entirely possible that planets with liquid water can exist outside the habitable zone. The real issue is with stability.
An interesting take on this is to consider the flux of radiation from the Sun hitting the Earth. For a disk the size of the Earth, one can calculate the distance where water freezes and where water boils as a rough estimate of a "zone" of sorts. When looked at in this way, the Earth is at a point just barely above freezing. That we have the climate that we do beyond that near freezing point is due entirely to greenhouse effects.

Mars had liquid water at some point and is outside the habitable zone, for some definitions of habitable zone. So it is entirely possible that planets with liquid water can exist outside the habitable zone.

Am I correct in assuming that the liquid which must have flowed on Mars doesn't necessarily have to be water, or has there been proof that the liquid was specifically water? That's a real question by the way, I'm not trying to be sarcastic. If anyone knows, I'd appreciate an answer.

I'm not aware of anything that's liquid at the right temperatures and pressures and likely to be available in a large enough quantity to substitute for water. The only possibility I can think of would be ammonia and it seems it would likely have somewhat different effects than water because of its reactive nature.

Mars had liquid water at some point and is outside the habitable zone, for some definitions of habitable zone. So it is entirely possible that planets with liquid water can exist outside the habitable zone.

Am I correct in assuming that the liquid which must have flowed on Mars doesn't necessarily have to be water, or has there been proof that the liquid was specifically water? That's a real question by the way, I'm not trying to be sarcastic. If anyone knows, I'd appreciate an answer.

The presence of water is proven on Mars. The existence of minerals that only form in the presence of water is proven on the surface of Mars. Massive liquid-based erosion is proven on the surface of Mars. Its reasonable to assume they're all related. And, frankly, the fact that water is found damn near everywhere in the solar system where it hasn't been torn apart by radiation, or heat makes is really implausible that there wouldn't have been water on Mars -- water that got there the same way it got to Earth, during a period of time in which Mars was more conducive to surface water than Earth.

IMO, the whole "finding water on Mars" thing is more akin to the "seeing a giant squid alive in the ocean". Everyone knows its there, but scientists just like to see things with their own eyes. The search is the fun part, so... search away.

This is interesting, since all the scientific data I've seen says that ultimately, Venus is far better than Mars as a target for Terraforming, yet this research is claiming that Venus is far outside the habitable zone, while Mars is smack in the middle of it.

Mars simply lacks two things: (1) the ability to generate a good strong magnetic field (too small, and no molten iron core), so it gets constantly bombarded with far more solar radiation than terrestrial life can stand outdoors, and (b) its much smaller mass and lack of magnetic field make is impossible for Mars to hold an atmosphere that's much more than it has now. So the result is that, while Mars superficially seems a better place for life now, there's no good way for us to transplant onto Mars without having to either live underground or under thick domes.

Venus, on the other hand, already generates a good magnetic field, and has no problem holding a significant atmosphere. It's just too hot and toxic. But a couple thousand tons of bacteria into the upper atmosphere will solve that problem, so Venus is actually the best candidate to turn into an Earth-like place.

I guess we'll have to look for two criteria: (1) which planets are most likely to have Earth-like indigenous life on them, and (2) which planets are best suited to be terraformed for occupation by us.

So exactly how does one eliminate a high pressure atmosphere from Venus? One way of lowering the atmospheric pressure is reducing the mass of venus (thereby having weaker gravity, and unable to hold a high pressure atmosphere), but say you managed to instantaneously precipitate half of venus's atmosphere into solid form, and reduced its atmospheric pressure by half -> wouldn't its gravity tend to move the atmosphere back into a high-pressure equilibrium with the planet?

You drop the temperature and all that atmosphere will come raining/snowing down. Probably the best way to drop the temperature is to unfurl a very large, semi-permiable membrane at the liberation point between Venus and the sun, to reduce the amount of solar flux reaching the surface. Eventually, we could do all that shading with a gigantic array of solar panels at L2 - just large enough so that the solar flux hitting the surface of Venus is the same amount as what hits the Earth (this requires 50% coverag

2. Even if it did, its day is about the same length in its year (e.g. about 250 earth days) so nobody could live in any fixed place on the planet without freezing or melting, even if we got rid of the thick atmosphere. You'd have to live in trucks rolling slowly around the planet in the... pardon the pun... twilight zone.

Mars on the other hand has normal days and could be warmed up with a greenhouse effect. Also, the thicker atmosphere would provide additional sheilding at the surface level. One could imagine the last few percentage points of shielding being made up with local magnetic field "bubbles" around settled areas, powered by fusion reactors, assuming we have that technology in the next century or so.

Yes, and fixing that would be something that requires several orders of magnitude more space capability than we currently have. Dome cities could be done which would have a pretty decent effect, but in the very, very long term, we could bombard mars with water rich asteroids from the asteroid belt. While I concede that this is extremely unlikely today, it's certainly a hell of a lot more feasible than removing the Venusian atmosphere and making Venus spin faster.

Venus, on the other hand, already generates a good magnetic field, and has no problem holding a significant atmosphere. It's just too hot and toxic. But a couple thousand tons of bacteria into the upper atmosphere will solve that problem, so Venus is actually the best candidate to turn into an Earth-like place

Venus doesn't have enough hydrogen to support hydrocarbon based life. Your cyanobacteria will simply die unless you hit Venus with a preposterous mass of comets. You may also need to get rid of the excess CO2 so your bugs don't they don't get too cooked.

Alas, you are wrong about Venus. It has a negligible magnetic field (likely due to no core convection) and cosmic rays and the soloar wind freely interact with the upper atmosphere causing hydrogen loss. As well, if Venus was a black body and had no incoming radiation it would take on the order of 600+ years to cool off.

It's True! I went on the sun deck on the rooftop of the building with the lockers at the local pool. It was 10 ft. up in the air and I got a terrible sun burn! that's because I was out of the habitable zone! Good thing I didn't go up there at night when the sun was on the other side of the world, I'd surely have frozen to death being outside the HZ

As the authors explain "Testing these predictions quantitatively using 3-D climate models should be a fruitful topic for future research." i.e. they need to keep paying mortgages, car loans,... next few years. The model is so embarrassingly inadequate, that considering how much room for fudging one has with toy models, they still barely managed to get Earth to come inside the "habitable zone."

I also wonder how will politicians translate this 1-D toy model into a story in which we are somehow responsible for

Simulation of being just a bit further away from the Sun sounds like it would effect what happened in the Maunder Minimum, with reduced Solar output where millions of people starved to death in Europe alone.

While everyone debates how many nukes it would take to adjust earth's orbit, I decided to see if our current solar distance under the new guidelines was actually a problem. I fired up Celestia [shatters.net] and although I'm not sure what kind of factors it takes in to effect at both a macro and micro level, I figured it would give a decent representation of our solar orbit trends for the next 10 millennium at least.

It looks like around Jul 16, 2013 we're at our farthest solar orbit of around 1.0164au and around December 31, 2013 we're out our closest solar orbit at around 0.98333au. Fast forward 11970 years and around June 30, 13983 we are at our furthest solar orbit of around 1.0151au and around December 30, 13983 we're at our closest solar orbit of around.98390au. And if you advance even further to over a million years in Celestia we're still looking at solar distances right around the same range.

Sure, the close range may mean that we're too close to the sun by only 0.00667au and our saving grace is that it won't stay at.98333au all year round, but somebody may want to inform the researchers that we are outside of their range and the earth appears to be quite habitable. And for the rest of you, let's not try to solve a problem that doesn't exist and won't exist for a very, very, VERY long time.

You're right, we shouldn't build models based on math. We shouldn't even try to understand the universe using such abstract tools. We should rely on thought experiments and push models around in sand. We can dress in togas and burn heretics.

He should not have published anything until his model matched up in some meaningful way with known facts about climate history. Obviously the lack of accounting for such a massive element is what probably is leading to this ridiculous idea that we're somehow almost too hot to support life, which is why we've had dozens of ice ages, including some which arguably devolved into 'snowball earth' scenarios where the virtually the whole planet was frozen. If your model doesn't fit major facts, it sucks, and it should be completely retooled at a minimum, or even discarded, because models that don't fit facts are nothing but incomplete masturbations.

I would think there would be more empathy for a collaborative approach around here. What he is doing is the open-source equivalent of putting an early alpha up on GitHub. Hell, he even offers up the source code [washington.edu].

You also have to take into consideration that the Sun is getting hotter, estimates are that it has got at least 25% hotter over the course of the life of the Earth. This is due to the ratio of helium to hydrogen changing causing the Sun to become more dense and therefore burn hotter. Estimates are that in as little as 500 million years the Earth will have its oceans boil and we'll become much more similar to Venus.Then there are variations in the Earths orbit, variations in the layout of the continents as w

Clouds not only affect sunlight on the day side of the planet but also also radiative heat transfer from the surface on both the day and night sides. Ever notice how much warmer it can be on a cloudy night than on a clear night? Current research indicates that clouds overall probably have a slightly positive effect on global warming but much research still needs to be done.

So clouds have an effect but greenhouse gases still dominate the equations. That affects the accuracy of model he uses but it's likely not an order of magnitude off and so is useful as a starting point to further refine the science.

This binary thinking that something has to be 100% right or it's completely wrong is not how science works.

Water vapor is the number one greenhouse gas in the atmosphere by a wide margin. It just doesn't persist there very long, and people can't seem to understand the concept of an "equilibrium", especially a changing one.

While I didn't mention water vapor except generically in greenhouse gases I agree with what you said.

However if get the feeling you may be conflating clouds and water vapor. Sorry if I'm wrong. They certainly are related since a cloud's existence depends on water vapor but the greenhouse effects of clouds and water vapor are quite different.

Umm... they are. Most granting agencies require scientists to do this.

Also, what exactly are you suggesting here? Big oil companies paid the scientists to place the earth at the hot edge of the habitable zone so that people would get more scared of it getting hotter? Or is this the "big solar" conspiracy theory again?

Why would moving further from the Sun warm the oceans? During much of the Earths history the oceans have been close to 40 degrees (80% is what I've read) but since humans have evolved during the current cold period it is questionable if we can survive in a world where the oceans are a couple of degrees above body temperature. Dinosaurs seem to have done well though.

It was only about 1 billion years ago, right before the first animal-like critters appeared. Thus, the figure is probably more like 10% dimmer. Still, that would keep Earth in the Habitable Zone described in the article. A dimmer sun would move the HZ inward.